COMPARISON OF ACID MIXTURES IN HIGH-PRESSURE MICROWAVE DIGESTION METHODS FOR THE DETERMINATION OF THE TOTAL MERCURY IN SEDIMENTS BY COLD-VAPOR ATOMIC-ABSORPTION SPECTROMETRY

Four closed-vessel microwave digestion methods were compared for the a ccurate determination of mercury in sediments by flow-injection cold-v apor atomic absorption spectrometry. The results showed that several a cid mixtures (HNO3/H2SO4. HNO3/HClO4, HCl/HNO3 and HCl/HNO3/HF) comple tely digested the soil matrix for the determination of mercury. The me thod using aqua regia is preferred because it is time saving. less dan gerous and suitable for other trace-metal analyses. The merits of pres sure-feed back microwave digestion is that it simplifies soil sample d igestion, and there is no loss of mercury. The digestion methods were evaluated by determining mercury in NIST SRM 1645 River Sediment, NIES CRM No. 2 Pond Sediment and NRCC BCSS-1 Marine Sediment. Recoveries o f 92 - 108% were achieved. Good recoveries of 94 - 104% were also obta ined for soil and marine-sediment samples spiked with different specie s of mercury.